It's something that Fluta, a bank clerk from Kosovo, knows only too well.
"Some of my friends wanted to go to Serbia, as they needed some medical treatment, [but] they couldn't go there as the only documents they had were the UNMIK documents," Fluta says.
In recent months, there has been a rise in the number of Kosovar Albanians applying for Serbian travel documents.
But authorities in Serbia do not recognize travel documents, identity cards, and other personal documents currently issued by the United Nations Interim Administration Mission in Kosovo (UNMIK).
"UNMIK has no right to introduce any kind of travel document."
"It is a well-known fact that Serbia does not recognize UNMIK documents, which they do not consider valid," Veton Elshani, a spokesman for the Kosovo police force, told RFE/RL.
To cross the administrative border, each traveler must carry a valid document issued by the former Yugoslavia or Serbia.
And in order to drive into Serbia across the administrative border in a vehicle registered in Kosovo, it is necessary to obtain temporary license plates and insurance for additional expense. Serbia does not recognize UNMIK driver licenses.
Recognized, But Not In Serbia
UNMIK, which has administered Kosovo since 1999, and other institutions in the province recognize all documents issued in Serbia.
UNMIK travel documents are recognized by 39 European and other countries. Serbia remains the only country in the region that fails to recognize documents issued by the international administration in Kosovo.
To get around the problem, residents of Kosovo intending to travel to Serbia for personal or business reasons often obtain identity cards or passports in Serbia itself.
The problems have been exacerbated with the return of migrant workers from Western Europe through Serbian border crossings.
"The Serbian authorities do not allow our citizens traveling to Kosovo from the direction of Montenegro, Albania, or Macedonia to use the administrative crossings, forcing them instead to pass through at least one state border, which means Macedonia or another state border crossing," Elshani says.
"Of course, these rules do not apply to holders of Yugoslav passports, who are allowed to enter Serbia without problems."
Business across the border has been less affected. Elshani says that the entry and exit of goods to and from Kosovo has been made significantly easier.
The Alliance of Kosovo Businessmen says that economic interests have prompted Serbia to issue the necessary documents to businesspeople.
"One reason is the need to secure a market for their products, and the second is a political reason," says the alliance's president, Agim Shahini.
Shahini says he believes that problems with the nonrecognition of documents have been created above all to prove that Kosovo remains a part of Serbia.
'No Easy Solution'
The problem has been frequently discussed by senior Serbian and UNMIK officials. However, Serbia's stance on the issue has not changed.
Vuko Antonijevic, the president of the Serbian government's Coordination Center for Kosovo, says that the government has every right to refuse to recognize UNMIK documents.
"UNMIK has no right to introduce any kind of travel document. Unfortunately the [Serbian] government was initially caught off guard, given that one set of officials should have remained in Kosovo to issue travel documents," Antonijevic says. "Freedom of movement is certainly a problem, but what can I do?"
Antonijevic says that all Kosovo residents are obliged to pay certain taxes when entering Serbia, primarily related to motor vehicles.
And according to Antonijevic, there is no easy solution.
"We cannot recognize their documents anyway, since they have refused to recognize ours, which they were bound to do until the status of Kosovo is resolved," Antonijevic says.
"They don't have a right to their own passports, nor identity cards and drivers' licenses. They wanted to invalidate Serbian documents in Kosovo, which the government could not accept. Everyone knows who is entitled to issue travel documents, and it is certainly not some sort of temporary mission -- Kosovo is not a state. This is against every convention, and all international rules -- it is perfectly clear who has the authority to issue travel documents."
A number of nongovernmental organizations have petitioned the Serbian government to recognize the UN documents issued in Kosovo.
Andrej Nosov from the Serbian-based Youth Initiative for Human Rights says that Serbian authorities have maintained double standards regarding UN Resolution 1244, which they cite in support of their refusal to recognize UN-issued documents.
"Serbia makes use of UN Resolution 1244 for one thing that is in its interest, while effectively refusing to recognize UNMIK, a UN-authorized body," Nosov says.
"This is not something that affects only people from Kosovo with UNMIK documents, but citizens of all countries who happen to arrive first in Pristina, through Pristina airport, and attempt to enter Serbia afterwards. They are impeded because Serbia does not recognize the UNMIK stamp that travelers receive upon entry into Kosovo," Nosov says.